thiL encodes thiamine-monophosphate kinase (EC 2.7.4.16), which catalyzes the ATP-dependent phosphorylation of thiamine monophosphate (TMP) to form thiamine pyrophosphate (TPP), the biologically active cofactor form of vitamin B1. ThiL is a homodimeric enzyme belonging to the PurM-like ATP-binding superfamily with a bilobal fold (N-terminal and C-terminal PurM-like domains). Structural studies on homologs from Aquifex aeolicus and Acinetobacter baumannii demonstrate that ThiL uses a direct in-line transfer of the gamma-phosphate of ATP to TMP, rather than a phosphorylated enzyme intermediate. The active site requires multiple magnesium ions and sits at the dimer interface. In M. jannaschii, thiamine biosynthesis uses a chimeric pathway with a eukaryote-like Thi4 (iron-dependent thiazole synthase) and bacterium-like ThiC (HMP-P synthase), regulated by the transcriptional repressor ThiR rather than a riboswitch. ThiL catalyzes the terminal step of this pathway, converting TMP to the active cofactor TPP. All current annotations for Q60337 are based on homology; no direct experimental characterization of this specific M. jannaschii protein exists.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000287 magnesium ion binding | IEA GO_REF:0000104 | ACCEPT | Summary: IEA annotation for magnesium ion binding based on UniRule transfer (HAMAP MF_02128). Crystal structures of ThiL homologs show multiple magnesium ions coordinating the phosphate groups of ATP and TMP in the active site. Sullivan et al. (2019) demonstrated that the transferred phosphate groups specifically require magnesium ions, while other metal positions in the active site show more plasticity. Reason: Magnesium binding is well supported by structural studies of ThiL homologs. Crystal structures from both A. aeolicus and A. baumannii confirm multiple Mg2+ ions in the active site. The M. jannaschii protein conserves all HAMAP-predicted magnesium binding residues. This is a core mechanistic feature of the enzyme. Supporting Evidence: PMID:30867460 a distinct variability of metal content of the active site PMID:18311927 Thiamin monophosphate kinase (ThiL) catalyzes the ATP-dependent phosphorylation of thiamin monophosphate (TMP) to form thiamin pyrophosphate (TPP), the active form of vitamin B 1. |
| GO:0005524 ATP binding | IEA GO_REF:0000104 | ACCEPT | Summary: IEA annotation for ATP binding based on UniRule transfer (HAMAP MF_02128). ThiL is a member of the PurM-like ATP-binding superfamily and ATP is one of the two substrates of the enzyme. Crystal structures confirm a deeply buried ATP binding pocket at the dimer interface. Reason: ATP is a direct substrate of ThiL. The ATP binding site is formed by conserved residues in the interdomain cleft of the bilobal PurM-like fold. Structural studies on homologs confirm ATP binding in this pocket. The M. jannaschii protein conserves the key ATP-binding residues predicted by HAMAP. Supporting Evidence: PMID:18311927 ThiL is a member of a small ATP binding superfamily that also includes the purine biosynthetic enzymes, PurM and PurL, NiFe hydrogenase maturation protein, HypE, and selenophosphate synthase, SelD. PMID:30867460 the ATP-dependent phosphorylation of thiamine monophosphate (TMP) to thiamine pyrophosphate |
| GO:0009030 thiamine-phosphate kinase activity | IEA GO_REF:0000120 | ACCEPT | Summary: IEA annotation for the core molecular function of ThiL, based on combined automated annotation methods including InterPro IPR006283, RHEA:15913, and EC:2.7.4.16. This is the defining enzymatic activity of the ThiL family: ATP-dependent phosphorylation of TMP to form TPP. Reason: This is the core molecular function of ThiL. The M. jannaschii protein matches all family-defining signatures (IPR006283, TIGR01379, PTHR30270, CDD cd02194) and conserves the catalytic residues. Structural studies on homologs demonstrate this activity proceeds via direct in-line transfer of the gamma-phosphate of ATP to TMP. Supporting Evidence: PMID:18311927 Thiamin monophosphate kinase (ThiL) catalyzes the ATP-dependent phosphorylation of thiamin monophosphate (TMP) to form thiamin pyrophosphate (TPP), the active form of vitamin B 1. PMID:30867460 Thiamine monophosphate kinase (ThiL) catalyzes the last step of thiamine pyrophosphate (TPP) synthesis file:METJA/thiL/thiL-deep-research-bioreason-sft.md A cytosolic enzyme that phosphorylates thiamine monophosphate using ATP to produce thiamine pyrophosphate, the active coenzyme form required for central carbon metabolism. |
| GO:0009228 thiamine biosynthetic process | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: IEA annotation for involvement in thiamine biosynthetic process based on InterPro2GO mapping from IPR006283 (Thiamine-monophosphate kinase-like). ThiL catalyzes the terminal step of thiamine diphosphate biosynthesis, converting TMP to TPP. While ThiL is correctly part of the thiamine biosynthetic pathway, the more specific term GO:0009229 (thiamine diphosphate biosynthetic process) better captures its role. Reason: ThiL is part of the overall thiamine biosynthetic pathway, so this annotation is not incorrect. However, it is less specific than GO:0009229 (thiamine diphosphate biosynthetic process), which directly describes the step ThiL catalyzes. The more specific term is already annotated. This broader term is retained as non-core since it provides useful pathway context via InterPro2GO but does not capture the precise biological role. Supporting Evidence: PMID:18311927 Thiamin monophosphate kinase (ThiL) catalyzes the ATP-dependent phosphorylation of thiamin monophosphate (TMP) to form thiamin pyrophosphate (TPP), the active form of vitamin B 1. |
| GO:0009229 thiamine diphosphate biosynthetic process | IEA GO_REF:0000120 | ACCEPT | Summary: IEA annotation for involvement in the thiamine diphosphate biosynthetic process based on combined automated methods (UniRule, UniPathway UPA00060). ThiL directly catalyzes the conversion of TMP to TPP (thiamine diphosphate), which is the sole step of this sub-pathway. Reason: This is the most specific and accurate biological process annotation for ThiL. The enzyme catalyzes the single step from TMP to TPP, which is precisely the thiamine diphosphate biosynthetic process. UniPathway UPA00060 step UER00142 confirms this is a one-step pathway. Supporting Evidence: PMID:30867460 Thiamine monophosphate kinase (ThiL) catalyzes the last step of thiamine pyrophosphate (TPP) synthesis, the ATP-dependent phosphorylation of thiamine monophosphate (TMP) to thiamine pyrophosphate. PMID:18311927 Thiamin monophosphate kinase (ThiL) catalyzes the ATP-dependent phosphorylation of thiamin monophosphate (TMP) to form thiamin pyrophosphate (TPP), the active form of vitamin B 1. |
| GO:0005737 cytoplasm | IEA GO_REF:0000002 | NEW | Summary: NEW annotation. ThiL is a soluble cytoplasmic enzyme with no transmembrane domains or signal peptides. The protein lacks any predicted export signals and the PurM-like bilobal fold is characteristic of soluble cytoplasmic enzymes. The BioReason SFT analysis also inferred cytoplasmic localization based on domain architecture. Reason: ThiL is a soluble enzyme that acts on cytoplasmic substrates (ATP and TMP). The protein has no transmembrane domains, signal peptides, or other localization signals. Cytoplasmic localization is consistent with its enzymatic role in the thiamine biosynthetic pathway, where substrates and products are cytoplasmic metabolites. Although no direct experimental localization data exists for this archaeal protein, the inference is strong based on protein architecture and pathway context. Supporting Evidence: file:METJA/thiL/thiL-deep-research-bioreason-sft.md the architecture lacks transmembrane segments or export signals and matches a soluble PurM-like bilobal enzyme, the most plausible cellular location is the cytosol |
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Download this section (compressed HTML)Q: Has ThiL from M. jannaschii been directly assayed for thiamine-phosphate kinase activity, and does the hyperthermophilic enzyme show any unusual kinetic or stability properties compared to mesophilic homologs?
Q: What is the physiological source of TMP in M. jannaschii -- does it use the canonical ThiE (thiamine phosphate synthase) or the bifunctional ThiDN?
Experiment: Express and purify recombinant M. jannaschii ThiL (Q60337) and perform in vitro kinase assays at thermophilic temperatures (65-85 C) to confirm thiamine-phosphate kinase activity and determine kinetic parameters. Compare with mesophilic ThiL enzymes to assess thermoadaptation.
Hypothesis: M. jannaschii ThiL will show optimal activity at hyperthermophilic temperatures (around 80 C) with kinetic parameters comparable to characterized ThiL enzymes from mesophilic organisms.
Experiment: Determine the crystal structure of M. jannaschii ThiL to compare the active site architecture with the known structures from A. aeolicus and A. baumannii, particularly examining metal coordination geometry at the higher physiological temperature of this organism.
Hypothesis: The M. jannaschii ThiL structure will reveal conserved active-site geometry with potential thermostabilizing features (e.g., additional salt bridges, compact hydrophobic core) compared to mesophilic homologs.
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